The present invention relates to a technique for enabling a flame retardant-containing resin composition to be recycled, and to a method for treating a resin composition by removing the flame retardant component to make it easier to reuse the resin.
Particularly, the present invention relates to a method for treating resin compositions containing a halogen-containing flame retardant, which are used as materials of the housings of, e.g., the monitors of televisions and computers, whereby their flame retardant components are removed therefrom and it becomes easier to reuse the resulting resins.
In recent years, there has been a desire for an effective utilization of resources, and techniques for recycling a variety of materials have been under development. Since resin materials such as plastics are generally disposed by incineration or land filling, it can be said that it is important to recycle waste generated during the production process of products and after their use. A variety of recycling techniques have been investigated from every possible aspect, example of which are thermal recycling in which resins are incinerated to provide fuels or combustion heat generated thereby is effectively utilized; chemical recycling in which resins are liquefied or gasified to provide starting material or fuels; other chemical recycling in which resins are decomposed to be recycled as oligomers or monomers which are starting materials of the resins; and materials recycling in which resins are pelletized as they are and reused. Ease of treatment and the quality of the resulting starting materials and fuels are important in these recycling techniques.
Generally, from the view point of safety, resins that are used for housings and substrates of household electric appliances are rendered flame retardant through incorporation of a flame retardant. For example, as materials of the housings for monitors of computers and video recorders, thermoplastic resins such as styrenic resin, ABS (acrylonitrile-butadiene-styrene) resin, high-impact polystyrene resin (blend of polybutadiene and polystyrene) with improved impact resistance are currently in general use.
However, thermoplastic resin themselves have the drawback of being highly combustible. Therefore, from the view point of prevention of the spread of flame in case of fire, flame retardant resin compositions which are rendered flame retardant by adding flame retardancy-imparting agents such as flame retardants or flame retardant auxiliaries to resins are in wide use. Of these, halogen-containing flame retardants are in global use, because they have the effect of imparting high flame retardancy to a variety of thermoplastic resins and are cheap.
When recycling these flame retardant resin compositions, there arise the problems that the presence of the flame retardant component makes the treatment of obtaining starting materials and fuels difficult and that the quality of the recycled product will be lowered as a result of mingling of the flame retardant component or the decomposed product. Therefore, particularly, almost no attempt to treat or recycle flame retardant-containing resin compositions has been made, presenting a serious problem.
Thus, for example, as a method of recycling a flame retardant resin composition, a method of thermally decomposing the resin with the flame retardant contained therein by thermal or chemical recycling has been investigated. Japanese Unexamined Patent Publication No. Hei 11-140223 discloses a method in which a plastic resin such as polyvinyl chloride is heated to eliminate the halogen component therefrom and then decomposed. Japanese Unexamined Patent Publication No. Hei 11-228731 discloses a method in which the resin is decomposed together with the flame retardant contained therein.
Moreover, in the case where a halogen-containing flame retardant is employed as the flame retardant, the halogen component contained therein is eliminated upon thermal decomposition in thermal or chemical recycling, resulting in the emission of a halogen gas or a halogen-containing compound such as halogenated hydrogen. Incineration of such flame retardant-containing resin has the possibility of generation of a hazardous halogen-containing compound such as dioxin. These halogen-containing compounds facilitate the corrosion of equipment for treatment or require sufficient equipment for preventing such hazardous halogen-containing compounds to be released to the air.
Moreover, in order to prevent the corrosion of a container, for the case where plastics such as polyvinyl chloride and polyvinylidene chloride are decomposed, dehalogenation of the plastics in advance has been proposed. For example, Japanese Unexamined Patent Publication No. Hei 11-116729 discloses a method in which a plastic is heat-treated in an organic solvent thereby to dehydrochlorinate the plastic and remove an obtained hydrochloride together with low-boiling point components obtained through the decomposition of the plastic. Moreover, disclosed in Japanese Unexamined Patent Publication No. Hei 11-140223 is a method in which the halogen atoms eliminated by the heating of a plastic are recovered and the resulting plastic is decomposed with the u s e of a supercritical fluid. Japanese Unexamined Patent Publication No. Hei 11-156378 disclose s a method in which, when a hazardous halogen-containing compound such as dioxin generated upon incineration of plastics is decomposed through supercritical hydration, halogens are neutralized by being mixed with a neutralizing agent.
As of now, for treating flame retardant resin compositions thereby to recycle them, many methods to chemically recycle resins through decomposition have been proposed, but not so many proposals have been made to materially recycle them. Since a reduction of energy required to recycle flame retardant resin compositions can be realized through material recycling, the technological development is important. For example, decomposition of resins through chemical recycling to provide their starting materials further requires energy for synthesizing resins, but it is highly possible that material recycling of them makes such application of energy unnecessary.
Moreover, conventional methods for treating halogen-containing resin compositions involve heat treatment for eliminating halogens, and the application of heat results in decoloration of the resins themselves, a decrease in molecular weight, or degradation due to crosslinking. Therefore, although the resins treated in such manner are suitable for use in chemical recycling through decomposition, from the view point of quality, they are not suitable for use in material recycling where the recycled products are reused as resins. That is, chemical recycling in which resins undergo thermal decomposition does not have such problem, but technological development to provide recycled products with improved quality is required for material recycling.
In view of such problems as have been faced in the prior art, an object of the present invention is to provide a method for eliminating the flame retardancy, which prevents an effective reuse of a flame retardant resin composition comprising a flame retardant and a resin. In other words, an object of the present invention is to provide a method for treating a flame retardant resin composition in which a flame retardant component(s) is removed from the flame retardant resin composition to leave a favorably reusable resin free from degradation by heat.
Another object of the present invention is to provide a treatment method, which makes it possible to remove a flame retardant component from a flame retardant-containing resin composition without degradation of a recycled resin due to heat treatment and facilitates reprocessing of the recycled resin. Particularly, the present invention provides a method capable of being smoothly performed in combination with a series of steps of pelletizing and powdering a thermoplastic resin.
The present invention relates to a method for treating a flame retardant resin composition comprising a step of bringing at least part of a flame retardant resin composition containing a resin and a flame retardant into contact with a pressurized fluid constituted of a solvent thereby to reduce flame retardancy of the flame retardant resin composition.
In concrete, this method can be performed mainly in two manners as described below.
In the first embodiment of the method, the flame retardancy of the above-mentioned flame retardant resin composition is reduced through extraction of the flame retardant therefrom by bringing at least part of the flame retardant resin composition into contact with the pressurized fluid.
In this case, it is effective that the method comprises a step of foaming the flame retardant resin composition by the use of the solvent constituting the above-described pressurized fluid after the extraction of the flame retardant.
In the second embodiment of the method of the present invention, a halogen-containing flame retardant is employed as the flame retardant and the flame retardancy of the flame retardant resin composition is reduced through dehalogenation by bringing at least part of the flame retardant resin composition into contact with the pressurized fluid.
In this case, it is effective that the method further comprises a step of reducing the flame retardant resin composition with the solvent constituting the above-mentioned pressurized fluid after the dehalogenation.
Further, it is also effective that the method comprises a step of foaming the above-described flame retardant resin composition with the solvent constituting the above-mentioned pressurized fluid after the dehalogenation.
In the method for treating a flame retardant resin composition of the present invention, it is effective that the solvent is carbon dioxide.
Particularly in the first embodiment of the method of the present invention, it is effective that the pressurized fluid described above contains an auxiliary solvent.
It is also effective that the pressure of the pressurized fluid is not lower than the critical pressure of the solvent constituting the pressurized fluid and not higher than three times the critical pressure.
It is also effective that the pressure of the pressurized fluid is not lower than half the critical pressure of the solvent constituting the pressurized fluid and lower that the critical pressure.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.